The present invention relates to force-transmitting, motion-transmitting or torque-transmitting arrangements in general, and more particularly to a force-transmitting arrangement for use in a hammer drill for transmitting forces from a chuck of the hammer drill to a tool element mounted therein.
There are already known various types of motion-transmitting or force-transmitting arrangements for use in various power tools for mounting selected tool elements therein. Among the known arrangements, there is also already known to provide an internal thread in a chuck or a similar connecting element of the power tool, and to form an engaging portion of the tool element which is to be engaged by or in the chuck, with an external thread which is complementary or compatible with the internal thread of the chuck.
So long as the connection between the chuck and the tool element is only subjected to forces which act only in the axial, only in the radial or in both the axial and the radial directions of the tool elements and which are non-cyclical in nature, the configuration of the threads is only of a minimum consequence, so that it is already known to use various threads, such as a standard thread, knuckle thread, rectangular thread or trapezoidal or acme thread, for connecting the engaging portion of the tool element to the chuck, when threaded connection of these components is selected.
It has also already been attempted to use a threaded connection as the force-transmitting arrangement between a chuck of a hammer drill and a tool element mounted therein. In this conventional connection, the threads of the chuck and of the tool element are configurated symmetrically, that is, the portions of the respective thread which are located radially outwardly of the mean effective thread diameter of the respective thread are of configurations which are the same as the space between those portions of the same thread which are located radially inwardly of the mean effective thread diameter, and vice versa. For this to be true, the flanks, the crests and the roots of the threads must be of mutually complementary configurations, on the one hand, but the flanks of the threads must also be equivalently configurated to the two sides of the mean effective thread diameter on the other hand.
Experience with this type of a connecting arrangement, or a force-transmitting arrangement, in use in a hammer drill, has shown that the external thread at the engaging end of the tool element is more susceptible to damage, particularly to shear, than the internal thread of the chuck of the power tool. This is true even in the event that the materials of the female portion of the chuck having the internal thread and of the male portion of the tool element having the external thread, are the same, and particularly when the material of the male portion of the tool element is more brittle or susceptible to fatigue or notch failure than that of the female portion.